The market for retreaded pneumatic tires is almost entirely a trucking market. In the trucking market, the carcass of a tire is expected to last several hundred thousand miles, and be amenable to having a new tread adhered to it several times. New truck tires are quite expensive, and are therefore bought with the expectation that their high initial costs are offset by the long service life of the carcass, and the low comparative cost of retreading.
A variety of procedures and different types of equipment are available for use in recapping or retreading pneumatic tires. One of the first steps in retreading a worn tire is to remove existing tread material from the tire carcass by a sanding procedure known as buffing. Next a layer of what is known as “cushion gum” is applied to the carcass. This layer of extruded uncured rubber may be stitched or adhesively bonded to the carcass. Next, a tread layer is applied atop the layer of cushion gum. In the cold recapping process, the tread is cured rubber, and has a tread pattern already impressed in its outer surface. The tire is then placed in an autoclave, and heated under pressure for an appropriate time to induce curing of the gum layer, and binding of the gum layer to the tread and the carcass. In the hot recapping process, the tread is uncured rubber, and has no tread pattern. The tire is then placed in a tire mold and heated under pressure for an appropriate time to cure the gum layer and the tread, and to cause the gum layer to bind with the tread and the carcass. [The term “cure” refers to the formation of cross-links between the elastomer molecules in the rubber compound].
The “cushion gum” layer binding the new tread to the old carcass can be relatively expensive. With present tire retreading techniques, this layer is typically 1 millimeter to about 1.5 millimeters thick. It would be an a great advantage to a retreading operation to reduce the thickness of this layer while preserving the strength and durability of the bonds between the tread, gum layer, and carcass.